A British startup has proposed combining the "maybe one day" technology of fusion power with the "slowly, slowly" tech of ion propulsion to create an engine capable of sending humanity to the stars.
The Register sat down with Richard Dinan, CEO of Oxford-based Applied Fusion Systems (AFS), to learn a little more about the …

Re: On the subject of wildly optimistic deadlines

yeah without the urgency of winning a war [i.e. Manhattan Project to get fission to work] fusion power is likely to be "researched" until the cows come home [with no results, "always more research"].

Of course, being "the guy" to make it work for realz is a true motivator for SOME scientists. Good luck getting that past the upper management bureaucracy that is perpetually funded by "research" grants.

In any case I worked the maths out on this quite some time ago.

In order to get propulsion to be efficient, you have to accelerate a large mass by a small amount, but if that amount is too small, the engine isn't efficient.

There's a point at which the amount of fuel you need, accelerated by the engines you can build, will be minimized for maximum acceleration for whatever mission you're running. I'm pretty sure NASA's "rocket surgeons" run these numbers a LOT.

To make up for that a hydrogenous material [like water or methane] would be used. You'd have to separate out the hydrogen fusion fuel from that, but no big deal. Then the engines get to use that fuel to product propulsion with the bulk of the hydrogenous material. And "some electricity" can be produced along the way. So yeah you'd have to run the engines occasionally to recharge the batteries [or use fuel cells, or both].

In any case, using current tech [that does not involve warp fields and wormholes] you'd need to produce a reaction engine (one that produces a given amount of energy from the fusion of hydrogen into helium, then transfers that as kinetic energy of the propellant), such that the energy produced becomes velocity of the propellant, and gives you an impulse for acceleration. All of that coupled against the total weight on takeoff [with 100% fuel load] etc. etc. etc. even if that 'take off' is in earth or lunar orbit.

Re: On the subject of wildly optimistic deadlines

Fusion has always been a decade or two away since I wad a small child, so it's easy to think any deadline to be optimistic. This time it "might" be real. Big improvements have happened to superconducting materials that make ITER somewhat obsolete, and it now seems that you can get the magnetic field density needed to make small fusion reactors viable. A thin film of superconducting material deposited on steel tape revolutionizes the way these things can be built. The steel not only gives mechanical strength, it's a also the only insulator required as it's conductivity is so poor compared to the superconducting film.

you heard that story about a turtle moving half way to it's destination with each step......?

I just meant that it's been pushed back continuously, if it is demonstrably 'working' in 2025 I will be surprised. If I am buying electricity that was generated using a Tokamak in the next 50 years I will be elated

Mission energy requirements....

This has "Investment scam" written all over it. I don't believe the chap expects his audience to understand the power requirements of Ion thrusters, or the engineering challenges of building a fusion reactor (on earth or in space.)

Hell, if you can build a fusion reactor in space, you probably have the capability to build small ones for powering cargo ships. There would be a *lot* of money in that, which could finance your mission to mars if that's what you wanted to do...

You only need roughly one kilowatt to power a single Ion thruster suitable for an unmanned interplanetary mission. You'll need two pairs of two thrusters, so that you can have one fail and still use a pair to keep the thrust acting along the main axis of the spacecraft. That means you have a power budget for thrust of 2 kW, which is easily within the ability of a sensibly sized solar panel, leaving plenty of power for communications and sciencey stuff. This power input gives you maybe 400 miliNewtons of thrust, so the craft, weighing maybe 6 or 7 Tonnes, accelerates quite slowly. (i.e. the same force as exerted on your hand by a couple of 2p coins being pulled downwards by gravity....)

If you want to move a bigger spacecraft, just add more solar cells and Ion thrusters. (There are some difficulties in making bigger Ion thrusters, although the efficiency could be improved if the engineering problems with scaling can be overcome..)

Re: Mission energy requirements....

As long as you are in the interplanetary space, that is you have escaped the practical extent of the gravitational field of Earth, even a solar sail will do the trick. Or you can use radioactive carbon as mentioned in here earlier, with a half life of about 5000 years.

To escape Earth's field you need a bit more oomph to get out in a reasonable amount of time. And that is where nuclear power might help.

Re: Mission energy requirements....

"To escape Earth's field you need a bit more oomph to get out in a reasonable amount of time"

If you want to accelerate quickly, it would be a lot easier to use a big chemical rocket than a fusion reactor, and would require getting less mass into orbit given our current understanding of how to engineer fusion reactors.

Would you invest in a fusion powered ocean going cruise liner, construction beginning next year? If not, then don't even think about investing in fusion reactors in spaaaaaaaaace.

Re: Mission energy requirements....

I agree, this sounds like an investment scam on much the same lines as the Moller Skycar or whatever it was Steorn were wibbling about.

The first step towards doing anything interplanetary is improving on rockets for getting stuff into orbit. The techno-beanstalk technology is about the only thing that will work here, and it is just about within our current technology. What you do is use normal rockets to get a hub station up to geostationary orbit, then you start lowering a line of super-strong cable down towards the ground, using some sort of counter-weight to stop it dragging the station down.

When you have a line from ground to geostationary orbit, probably terminating at an artificial island in the Pacific, you start reinforcing this until you can send loads of a few tonnes from ground to geostationary orbit. At this point your costs of getting stuff from ground to orbit drop by a couple of orders of magnitude, and the safety of doing so increases tremendously. At this point, space tourism becomes possible (you have to be thinking of the money-making aspects of all of this), lunar colonisation becomes much easier, and once you have a moon base a mission to Mars becomes a going proposition as well.

The whole problem here is that space, even low earth orbit, is hostile to humans. We need complex life support to live up there and even then, solar storms emit huge amounts of radiation. Humans off the surface of the earth need somewhere to hide, and a few tens of metres of lunar regolith are one good place to be. The moon is a good jumping-off place for interplanetary missions because there's almost no atmosphere and much lower gravity; you can build complicated stuff on the surface there which can get to lunar orbit quite easily, and thence to interplanetary space, but on the moon is a much more forgiving place for humans than is free fall.

Once you have your beanstalk, lunar base etc then you can start looking to get to Mars. At this point I'm not really seeing a reason for not using the Orion drive; it works, it is simple and away from Earth radioactive contamination is going to get pushed away on the solar wind.

Re: Mission energy requirements....

"Once you have your beanstalk"

*If* someone had a credible material for a beanstalk, it would be being built right now. The trouble is we're not just talking about huge tensile and shear strength, we need a safety factor on those strength values of about 6 to allow for manufacturing variability, wear and tear and general cock-ups in predicting weather patterns.

We don't even have a plan to keep the orbiting end stationary:- thermal expansion and contraction of the beanstalk will cause variations in the orbital altitude of the top end, meaning that it will have to be constantly firing thrusters to stay above the base station, *assuming there is no wind*. The beanstalk would be situated at the equator, and would have to withstand hurricane force winds sometimes... You *could* use gas turbines distributed along the beanstalk to counteract the wind load, but then you just made it a lot heavier, requiring more tensile strength and creating a rather unique fuel distribution problem....

Re: Mission energy requirements....

Re: Mission energy requirements....

>If you want to accelerate quickly, it would be a lot easier to use a big chemical rocket than a fusion reactor, and would require getting less mass into orbit given our current understanding of how to engineer fusion reactors.

Correct, given the constraint you equally correctly identify. My point was rather more forward looking, to the time when fusion power was available, in which case a fusion equivalent of NERVA would be feasible.

Re: Mission energy requirements....

@AC - slight correction: solar power isn't much use beyond Mars because the energy collectable for a given area of solar collector decreases as the square of distance from the sun.

It took solar-powered Dawn, with its 36 sq.metre solar panels, dry mass of 747kg and 425kg of xenon propellant at launch, 15 months to get from Earth orbit to Mars and a further 29 months (plus a gravity slingshot from Mars) to get to Vesta. While its enormous solar array provided 10 kW in Earth orbit (1AU radius), this had dropped to 3kW at 3AU. Vesta, its first target, orbits at 2.15 AU from the sun. It then took another 30 months to get from there to Ceres,which orbits between 2.56 and 3 AU from the sun.

I think this shows that Ceres at, a bit under 3AU from the sun, is about the practical limit for solar powered spacecraft. The next planet out, Jupiter, is at 5.2AU, so if Dawn was orbiting Jupiter, its solar cells would only be providing 1kW.

Re: Mission energy requirements....

Not *relevantly* true with current technology because:

Solar radiation to power the solar panels falls off as 1/r^2, which means your ion engine has produced most of the delta-v it is ever going to, by the time it has gone more than 0.5AU outwards from the Sun. Your standard 400mN thruster achieves 0.6mm s-2 on a 6 tonne spacecraft. Unfortunately, that only gives you a delta-v of about 5-8 km/s. That’s *good*, but it certainly isn’t a game-changer compared to conventional chemical.

To be a game-changer for delta-v, it would have to accelerate *much* faster over the “runway” of the first 50 million km outwards from the Sun. 3-5 mm/s2 at least. That means much higher power requirements, so very much larger solar panels (mass starts to exceed what we know how to fold away in the launcher), and plain beefier ion thrusters.

But god knows why fusion......

Actually a standard nuclear RTG is just the ticket to generate electricity independent of distance from Sun and therefore a much longer “runway”. Just, we aren’t allowed to launch RTGs any more for political and environmental reasons.

Re: Can't we send them off right now?

What's in a name?

The man dislikes the word 'nuclear' as he says people think 'bomb'. He has named his mini-tokamak STAR where A stands for Atomic. I've just tried the word association game with a few friends and 'Nuclear' gives 'Reactor' as the usual response, but 'Atomic' was 'Bomb' in every single case. Either Dinan is much mistaken or it says something about my circle of friends.

Re: What's in a name?

>I've just tried the word association game with a few friends and 'Nuclear' gives 'Reactor' as the usual response, but 'Atomic' was 'Bomb' in every single case. Either Dinan is much mistaken or it says something about my circle of friends.

That could be something about your circle of friends. My experience is that

- if you are a physicist you automatically become responsible for nuclear weapons, in all countries, and you are about to end the world in a nuclear Armageddon.

- if you are a chemistry graduate you automatically become responsible for pollution, in all countries, and you are about to cause the end of the world by ozone hole depletion, global warming and drowning in waste

- if you are a biologist you automatically become responsible for GMO, in all countries, and you are about to cause the end of the world by hideous deranged mutant monsters.

One of my friends therefore always said he was a upholsterer when people asked him what he did for a living.

Re: Interstellar fuel

Re: Interstellar fuel

Would be a good idea to get ion thrusters to use methane as a fuel... Capture the farts of the spacefarers, and use it for propulsion!

A number of propulsion systems utilizing wastes from the ISS's life support have been seriously considered. It isn't unusual for waste systems optimized to recover oxygen (from CO2 or water) to end up with waste methane, hydrogen, and/or carbon that could be adopted to ion- or arcjet propulsion.

Want to travel to the stars then get digging and look for a Stargate, the odds are better than us perfecting fusion before the Sun expands. Been hearing nonsense about fusion since Zeta was supposed to give us unlimited fusion power by 1970.

Was he an AI expert last week

Quite a bit of nuclear fallout

"While Orion, which could have lofted immense amounts of mass at the cost of, er, quite a bit of nuclear fallout, was axed in the 1960s"

Actually, no. The quantity and quality of fallout from a modern-day Orion using the cleanest warheads we know how to build would be minimal, vastly less even than the single small device used on Hiroshima. Launched from a remote location, most of the pulse-bombs detonated at altitude, with careful pauses for different layers of the atmosphere, you could get a massive Orion into orbit with negligible environmental impact. I think the most recent analyses suggest that a big Orion (say, something big enough to put an entire self-sustainable colony on Mars in a single voyage, supplies and all, maybe a 25,000-tonne ship) could be launched for the statistical "price" of one or two extra cancer cases worldwide.

Put another way, the solid science behind pollution analysis tell us that we could colonise the entire solar system with dozens of Orions and thousands of people, for about one-fortieth of the environmental impact and increased disease/death rate caused by Volkswagen cheating its emissions tests. And you could build the fleet of ships and pulse-bombs for about four times what VW has lost because of that same fraud. Any of the top twenty armed nations' miltary budgets could handle sedveral Orion missions if turned to exploration. The UK could swap Trident for Orion and have money to spare; along with bragging rights for the first serious spaceship ever flown. Oh, and immediate global dominance.

Indeed, if the benefit of an Orion fleet is decreased pollution and greater wealth on Earth—through building orbital and Moon-based solar power arrays; pulling metal-rich asteroids into the Earth-Moon system for mining; moving the worst polluting industries up into space—then we are insane not to do it. The likely benefits of Orion to our species so vastly outweigh the possible downsides that, from an economic and scientific point of view, we are verging on suicidal stupidity by ignoring this opportunity.

We don't even need to invent any radical new tech. Orions are surprisingly basic and easy to build. Even the pusher plate survives nuclear hammering much better than you'd imagine (mild ablation can be tolerated), and for sure we know how to build tidy, tiny warheads with precision launch and detonation ...

Orion sits there as a stunningly obvious, practical solution to spaceflight and arguably our best chance of survival as a species. We ignore it because of the N-word: in almost complete, oblivious, witless ignorance and foolishness.

Re: Quite a bit of nuclear fallout

a big Orion (say, something big enough to put an entire self-sustainable colony on Mars in a single voyage, supplies and all, maybe a 25,000-tonne ship) could be launched for the statistical "price" of one or two extra cancer cases worldwide.

But before you launch your colony ship, you certainly have to make numerous test launches, some of which will fail (quite spectacularly!)

For probaly the only situation where Orion might be feasible to push through (for desperate reasons), see "Footfall" by Niven and Pournelle.

Re: Quite a bit of nuclear fallout

"I think the most recent analyses suggest that a big Orion (say, something big enough to put an entire self-sustainable colony on Mars in a single voyage, supplies and all, maybe a 25,000-tonne ship) could be launched for the statistical "price" of one or two extra cancer cases worldwide."

That's really interesting. Do you have a source for that? I'm fervently pro-nuke myself and I'd love to have that in my, ahem, arsenal.

Re: Quite a bit of nuclear fallout

Freeman Dyson did the calculation in the early 60s. There will be discussion of the calculation's result in his son's memoir "Project Orion: The True Story of the Atomic Spaceship", but as I recall, not of the calculation itself

There wouldn't be any fallout

At least I always presumed that the "exploding nukes to generate thrust" part only occurred in space, and that conventional rockets would loft it into space first (probably a bunch of them, to assemble a larger craft in space) I think the bigger concern for most would be the risk involved in launching rockets filled with nukes. Even though we can now make them safe so that an explosion or ground impact won't make them explode it isn't risk free. To say nothing of convincing the public that they won't explode - a public where a non trivial number believe the Moon landings were faked.

Though I think the biggest flaw with Orion is getting much thrust out of a nuke. They have a lot of power, but even if you could direct all the charge at the back of the spacecraft, what the hell are you going to build the back out of for the nuke to push against that won't be destroyed in the process? If you used something designed to ablate somewhat with each charge, then your starting mass will be much larger and first nukes less efficient.

Re: There wouldn't be any fallout

Check out some of the pictures of underground nuclear explosions where they manged to get a camera into the cavity created.

Even for a 20kiloton nuke its not very big , now stand that off about 50 feet behind your pusher plate, while making sure the damper system between the pusher plate and the main body of the spacecraft is working.

And away you go..... also it helps to have a pusher plate that weighs about 6000 tons.....

The only drawback for launching a 25000 ton spacecraft is..... who wants to ride the first one into orbit.....

Re: There wouldn't be any fallout

At least I always presumed that the "exploding nukes to generate thrust" part only occurred in space, and that conventional rockets would loft it into space first

The original idea was indeed to go with the nukes all the way. The spaceship would have been huge, on the scale of a battleship, not aeroplane.

what the hell are you going to build the back out of for the nuke to push against that won't be destroyed in the process?

The Orion project scientist had this and a lot of other details worked out. Remember they had access to data and experience about nuclear bombs. The blast is powerful but not infinitely so, and with the data available to them, making a pusher plate that can survive multiple explosions is just a matter of engineering. The bombs would also have been precisely designed for the purpose.

Re: There wouldn't be any fallout

They have a lot of power, but even if you could direct all the charge at the back of the spacecraft, what the hell are you going to build the back out of for the nuke to push against that won't be destroyed in the process? If you used something designed to ablate somewhat with each charge, then your starting mass will be much larger and first nukes less efficient.

Dyson's concept, evaluated with plasma pulses against assorted targets, was that a plain steel pusher plate for a 6,000-ton surface launched vehicle would experience less than a millimeter of erosion. Larger, higher velocity interstellar Orion vehicles assumed the use of some sort of grease or water as an ablator, or used VERY large copper pusher plates that could handle the heat load and cool between pulses.

And note the nukes aren't bare nukes. They also include a substantial reaction mass to capture more of the nuke's energy and, at the same time, reduce the temperature of the pusher plate. Dyson planned on using disks of tungsten for a propellant.

Re: Quite a bit of nuclear fallout

" Launched from a remote location, most of the pulse-bombs detonated at altitude, with careful pauses for different layers of the atmosphere, you could get a massive Orion into orbit with negligible environmental impact."

I dunno, having worked in the nuclear industry I have this nagging desire to keep the fission products out of the atmosphere... [they really ARE pretty nasty]. It's why we don't use A-bombs nowadays for any kind of major excavation project.

Sure, it'd be "convenient" to blast open a canal with 10K-ton atomic bombs, but I think I'd rather put a few industrial diggers in there instead, and do it the "somewhat old" fashioned way.

And there's no reason why Orion-style nuclear propulsion can't be done out in space. Just not inside of Earth's atmosphere. It's basically why we need efficient launch systems, to get that stuff into orbit where it can be assembled safely and operated without impacting anyone on Earth.

Re: Quite a bit of nuclear fallout

Isn't cost also the reason why big construction projects aren't dug with nukes? After all, really big conventional explosives can make pretty big holes, but when explosives are used they are typically used in measured quantities and only when you need to get through solid rock. No one is using explosives to make a hole in soil, they use good old fashioned backhoes and dump trucks. Presumably because it costs less (if not the initial cost, when you figure in all the safety issues etc.)

I don't know what it costs the US government to build a nuke, but you can probably rent a small army of construction equipment for a fraction of that.

How much smaller?

Don't tell AUstin Texas!

Austin became the laughing stock, or something when they declared the town a "Nuclear Free Zone" in the 1980's.

I guess no one should tell them about the rather decent sized Tokamak in the sub-basement of one of the Engineering school buildings at University of Texas that has been successfully running for decades!

Re: Don't tell AUstin Texas!

Re: Don't tell AUstin Texas!

University towns like Austin that declare themselves nuclear free zones can't control what happens on property owned by the state government (i.e. University of Texas) or the federal government (military bases) Most of the people passing the laws knew this going in, and that it was only a symbolic gesture.

The state and feds are the only ones outside of utilities that do anything that would run afoul of such laws. It isn't like small businesses or individuals are allowed to have anything to do with nuclear technology, so a nuclear ban has as much impact on them as banning them from launching spacecraft within the city limits.

Wonderful?

Re: Wonderful?

If electric cars were powered by fusion reactors, and not fission, nor coal, nor oil/gas [as they mostly are now], then the anti-freedom crowd [in the name of the environment] would find some OTHER reason to whine about it and convince gummints to curb our freedom [but not theirs, of course].

Seriously. You know I'm right.

But I'd love to see fusion reactors making electricity. It would make electricity COST LESS.

Nukes in Space

So first to show the enormous cost of the project according to Nasa it spends around $6000 to send something the size and weight on a Lemon into space.

Second say you get this project up there and light the touch paper, how the hell are you proposing to slow such a mass going at the speeds you need for interplanetary travel ,create an stable orbit then fire off again to the next planet of interest as each would take days?

Not only that but the maths required for such navigational feats to hop planet to planet would be astronomical bearing in mind your "road map" is made from a telescope based on a planet millions of miles from where you are.

Thirdly what are the occupants going to survive on in regard to Air and food or is this going to be a one way journey?

[Quotes from google] :

How long did it take for Voyager to get to Pluto?

Launched in 2006, New Horizons is the fastest spacecraft to ever leave Earth. It crossed the orbit of Jupiter the next year and has been traveling nearly a million miles a day—but it still took 9.5 years for the spacecraft to reach Pluto and its moons.

What speed was the speed of the New Horizon satellite

The Jupiter flyby increased New Horizons' speed by 4 km/s (14,000 km/h; 9,000 mph), accelerating the probe to a velocity of 23 km/s (83,000 km/h; 51,000 mph) relative to the Sun and shortening its voyage to Pluto by three years.

When you look at it your propulsion is only a tiny part of the problem

Dead Horse flogging

Tokamaks? That's 1950's Soviet era tech. All you're ever going to get out of one of those is a bang in a bottle. Some form of focussed pinch field device might just work continuously, but not Tokamaks, no matter how big you build them.

As to pusher plates

timelines

"the Large Hadron Collider did not send the world screaming into an artificial black hole 10 years ago." Not in my timeline (and presumably not in yours, if you're reading this). But in a zillion other timelines, we're all gone.